fix(module:input): fix ng-content [nzAddOnBeforeIcon] content projection

[CygnusRoboticus]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features) N/A

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Projected content inside of an <nz-input-group> disappears when [nzAddOnBeforeIcon] is updated.

Issue Number: #3596

What is the new behavior?

Projected content is displayed, [nzAddOnBeforeIcon] behaves correctly.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

I attempted to add tests, but I find angular testing difficult and could not come up with something satisfactory for projected content.

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[codecov]

Codecov Report

Merging #3597 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3597      +/-   ##
==========================================
+ Coverage   95.72%   95.73%   +<.01%     
==========================================
  Files         690      690              
  Lines       13708    13708              
  Branches     1824     1824              
==========================================
+ Hits        13122    13123       +1     
  Misses        198      198              
+ Partials      388      387       -1

Impacted Files	Coverage Δ
components/time-picker/time-holder.ts	97.26% <0%> (+0.68%)	⬆️

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[vthinkxie]

LGTM